The invention relates to truck trailer couplings that are slidably adjustable, such as extendable reach-type tongues and, more particularly, to remotely operated locking devices for releasably locking the coupling in each of its adjustable length positions.
Extendable reach tongues provide a needed versatility that is not available from trailer tongues having a fixed length. Restrictions have been imposed on many roads and highways as to the permissible gross weight of a truck trailer rig. These restrictions are, in part, based on the number of wheel axles and the separation between the axles along the length of the roadway. As the spacing between the axles increases, there is a corresponding increase in the permissible gross load per axle. Thus, by using an extendable reach tongue, a truck trailer rig can be spread out over a greater length of highway, thereby enabling the rig to carry a greater load. For highway travel, the extended length of the truck trailer rig is perfectly safe and sufficiently maneuverable.
However, for in-town driving of an unloaded rig, and for maneuvering in confined areas during loading and unloading operations, the extended length of the tongue is a disadvantage, and in some driving situations is totally impractical and/or unsafe. But, with an extendable reach tongue, the driver can adjust the length of the tongue to adapt his rig to the existing driving condition.
Extendable reach tongues of the above type are usually made of a pair of elongate, telescoping members that are equipped with locking mechanisms for releasably locking the members in either the shortened or extended position. In some cases the locking mechanisms are manually operated by means of a handle, shear pin, screw clamp, binding cam or the like mounted on and operable at the tongue. Since the driver must get out of the cab and walk back to the trailer tongue each time he either engages or releases the locking mechanism, it will be apparent that each time the tongue is to be extended or shortened, the driver will twice be required to leave the cab and walk back to the tongue.
To overcome this inconvenience, extendable tongues have been developed which are equipped with remotely operated locking devices. For example, one known system employs solenoids, remotely operated from the cab, to move a shear pin mounted on the outer tongue member, causing the pin to engage and disengage appropriately spaced pin receiving holes on the inner telescoping member of the tongue. Although such remotely operated locking devices do provide greater convenience and efficiency in the use of the adjustable length reach, they have not proved to be as durable as needed to withstand the adverse environmental and operating conditions normally encountered.
In particular, known types of remotely controlled locking devices typically employ a mechanism that, while locking the telescoping tongue members against any relative lengthwise sliding movement, allow such play between the tongue members and the pin or other locking element that the various parts are subject to excessively large impact loads and fatigue-causing metal-to-metal vibration. The impact loading occurs each time a tension or compression load is abruptly applied to the tongue, and the vibration loading occurs during road travel. These operating conditions have been found to cause, in too many instances, premature failure of the locking mechanism and the portions of the tongue members which cooperate with the locking mechanism.
Premature failure of a tongue locking mechanism during use of the rig constitutes a serious potential hazard. If, for example, a shear pin failed while the tongue was in a shortened configuration, the trailer may, under some circumstances, move uncontrollably and rapidly to the extended position of the tongue, or vice versa, and possibly cause injury to persons or property.
Both the remotely controlled locking devices, and those locking devices that are manually operated at the tongue, have the additional disadvantage of being located exteriorly of the tongue and thus exposed to damage from weather, rocks and other debris kicked up from the wheels of the truck while moving, and from other physical abuse normally encountered in the use of truck trailer rigs of this type. The vulnerability of exteriorly disposed locking mechanisms or associated components on available tongues of the extendable reach-type, has especially diminished the success and industrial acceptance of remotely controlled locking mechanisms which are usually more delicate and susceptible to damage under the above noted conditions.
Accordingly, one object of the invention is to provide a remotely operated locking mechanism for an extendable reach-type truck trailer tongue that is rugged, durable, safe and is capable of providing long trouble-free life.
A related object is to provide such a locking mechanism which is mounted with respect to the tongue so as to be sheltered from the environmental elements, and shielded against the type of physical abuse normally encountered in the use of heavy transport equipment.